Ludlow



Sept. 24, 1963 E. LUDLow souND ATTENUATING GAS PIPE 2 Sheets-Sheet l Filed Nov. '7, 1960 INVENTOR. ND LuDLow,

ma TMA i ATTORNEYS.

sept. 24, 1963 E. LuDLow 3,104,733 souND ATTENUATING GAS PIPE Filed Nov. 7, 1960 2 Sheets-Sheet 2 l\` l /l l? I s UVQ INVENTOR.

fEDMuND LuDLow *y By ATTORNEYS,

United States Patent() 3,104,733 SUND ATTENUATING GAS PEE Edmund Ludlow, Columbus, Ind., assigner to a Arvin industries, inc., Columbus, Ind., a corporatlon et indiana Filed Nov. 7, 1960, Ser. No. 67,756 16 Claims. (Cl. lim-48) This invention relates to a sound attenuating pipe, and more particularly to a sound attenuating exhaust pipe for use in association with internal combustion engmes for conveying the exhaust gases therefrom and for attenuating the noise level of said exhaust gases.

It is an object of my invention to provide a sound attenuating pipe which will convey the exhaust gases emanating from an internal combustion engine, which will attenuate the noise level of such exhaust gases, which will effect such sound attenuation over a wide range ot frequencies, an-d which can be tuned to attenuate any desired range of frequencies. It is a further object of my invention to provide a pipe having such sound attenuating properties which can be easily and economically manufactured from metal-tubing, which will have limlted space requirements, and which will provide an effective thermal insulation for hot exhaust gases.

In carrying out my invention in its preferred form, I provide an outer pipe having a plurality of inserts mounted therein, said inserts being coaxially aligned and deiining a main gas-flow passage throughout their length in the outer pipe. Each of said inserts comprises an elongated tube section having an outwardly projecting bell at one of its ends and a slightly constricted neck at its opposite end. In assembly, the neck of one of said inserts is press-tit into the tube section of the next adjacent insert lto thus form a substantially continuous main gasilow passage. The bell on each of the inserts abuts the inner wall of the outer pipe, and with the ends of the adjacent pairs of inserts in intertting engagement, each of said bells will thus support the adjacent ends of a pair of adjacent inserts in spaced relation to the inner wall of the outer pipe. Thus, each adjacent pair of inserts acts in `corrrbination with the adjacent wall of the outer pipe to dene a resonating chamber volume.

The inserts are provided With `elongated grooves formed in their restricted necks and, with each lof said necks being received in the tube section of the next adjacent insert, said -grooves and tube sections thus dene elongated throat passages to `dispose the resonating chamber volumes in operative communication with the main gas-flow passage whereby said volumes will effect an attenuation lof the noise level of the exhaust gases.

Other objects and features of my invention will become apparent `from the more detailed description which follows and from the accompanying drawings, in which:

FIG; l is an isometric view partially in section showing a sound attenuating exhaust pipe embodying my invention;

FIG. 2 is an enlarged fragmentary longitudinal section of the pipe shown in `FIG. 1 taken in the plane of the line 2 2 of FIG. 3;

FIG. 3 is an enlanged vertical section taken on the line 3 3 of FIG. 2;

FIG. 4 is an enlarged isometric view of one of the inserts shown in FIG. 2;

FIG. 5 is an enlarged fragmentary longitudinal section of a modified form of my invention and taken in the plane of line 5--5 of FIG. 6 with Ithe openings lying in the fnont of said plane being sho-wn in dotted line;

FIG. 6 is a vertical section taken on the line 6-6 of FIG. 5; and

FIG. 7 is an enlarged isometric view of one 0f the inserts shown in FIG. 5.

In the yoperation ot a conventional internal combustion engine in an automobile, the combustion 'of fuel within the cylinders produces a substantial volume of hot exhaust gases which are exhausted with substantial noise into one or more exhaust manifolds in communication with the exhaust ports of the several cylinders. The frequencies of the sound waves in such exhaust gases extend over a wide range, such as for example from about 30 cycles per second to about 5,000 cycles per second, and in many exhaust systems it is the lower range of frequencies, i.e., frequencies below 20() cycles per second, that are the -rnost diicult to attenuate or silence. This low range of frequencies below 200 cycles per second .is the most difficult to attenuate because the firing frequency of the engine falls within this range as does the natural resonance frequency of the exhaust system itself.

In a conventional automobile exhaust system, all of the silencing of the gases occurs in a muiller connected between an exhaust pipe joined to the exhaust manifold and a tail pipe leading `from the muffler to a gas discharge point. Such mullers conventionally comprise an outer shell having an elliptically `or circularly shaped cross-section several times larger than the cross-section of the exhaust pipe, and having a relatively small number of tuned resonator chambers adapted to attenuate the noise level of the exhaust gases passing therethrough. In order for the muler to achieve maximum silencing it is necessary that a pair of these chambers with large volumes be tuned to attenuate the narrow bands of the wave frequencies of the first overtones of the standing waves of the exhaust and tail pipes. All of these resonator chambers in the mutller are baffled from one another, and are arranged Within the outer muiller shell in staggered patterns which, combined with the large volumes of the chambers for the exhaust and tail pipes, results in the muffler being rather large and diicult to mount within the limited space available on the underside of an automobile.

My invention is yadapted to attenuate the noise level of the exhaust gases over ia Wide range of frequencies by passing said gases through a pipe construction containing a series of in-line inserts which provide a large number of small sound attenuating units disposed along the length of the exhaust system. These units are tuned to attenuate diiferent, and overlapping, bandsvof wave frequencies so that the combinative effect of all or the inserts is an attenuation of the entire range of frequencies of the sound waves in the exhaust gases. While my invention may eiect such yan attenuation of the exhaust Igas noises alone, if desired, it may also be used in combination wit-h other yin-line resonators, or a conventional mutller, or incorporated within a muler as a muliler component, or in combination with an acoustical liner, such 4as is [described 1in copeniding application Serial No. 67,527, led November 7, 1960.

As shown in FIG. 1, my invention comprises an outer pipe 1li `adapted to be connected lat one of its ends to an exhaust manifold by a conventional mounting ange 12. Conveniently, the pipe lll may have the same outer diameter of about 2.25 inches as is normally used in the exhaust pipes 'and tail pipes 'in conventional exhaust systems.

Mounted within lthe outer pipe l@ are a plurality of inserts 14 conveniently formed lof lengths of metal-tubing. As shown, each of said inserts comprises an elongated tube section 16 having an annular outwardly projecting bell 18 at one of its ends. Arr elongated open-ended constricted neck 20 projects yaxially from the opposite end of the tube Section 16. 'Ilhe outer diameter of the neck 20 approximates the inner diameter of the tube section may be stepped down, in which case the neck Ztl will not have a restricted diameter, but due to the stepped down tube section diameter, the neck of one insert can still be press-fit into the tube section of an adjacent insert (said Y alternative not being shown in the drawings).

in the assembly of my exhaust pipe, the series of inserts lll lare interconnected in the manner just descr-ibed, and are then forced into the outer pipe l() into a position such that said inserts will lie within the extent of the straight sections of said outer pipe. The tube sections ld and necks Ztl of the inserts are held in spaced relationship to the inner wall of the pipe lll by the outwardly projecting annular bells 13 which abut the inner wall of the pipe l0. As shown in FIG. 2, each of the bells l supports the end of the insert 14 upon which said bell is formed and the neck 'end of the next ladjacent insert. With the inserts thus supported in spaced-relationship to the pipe l0, each pair of adjacent bells 18` deli-nes the end walls of a resonatingchamber volume 22 having the conguration of an extended annulus, the side walls of said volumes being -formed'by the outwardly presented walls of the inserts 14 and the inwardly presented wall of lthe pipe llt). As will be apparent, the volumes 22 also CFI serve as a thermal insulation forthe exhaust gases passing through the inserts 14, and will lfurthermaterially reduce the direct transmission of high yfrequency sound from the gas stream through the wall of the outer pipe.V

The throats for the volumes 22 are formed by one or more grooves-formed in the necks 20 and/or ,tube sections l of the inserts. ln the illustrated embodiment of the insert,a pair-of inwardly projecting, radially spaced grooves 23 and 24 of unequal length are formed inthe neck 2d, the groove 24 extending the length or said neck and the groove 23 extending only approximately one-half the length of said neck. Conveniently, an outwardly projecting, `axially extending bead or :groove 25 is also formed in the tube section 16 adjacent the bell 18. As will be understood, the neck port-ions forming the edges of the ygrooves 23 and 24 bear against the walls ot the tube sections 16 of thenext adjacent inserts to thus `form axially extending volume throats interconnecting the main gas-ilow passage with the resonator chamber volumes 22. Because the insert necks Ztl are press-lit into the tube Y sections lo of adjacent inserts, it is of course possible to adjust both the volume of the resonating volumes 22 and the length, cross-sectional area, and number of the volume throats formed by the grooves 23-25 so that the volumes 22 will attenuate a wide range of sound frequencies. For example, if the neck Ztl of one of the inserts is forced la substantial distance into the tube section of the next adjacent insert with its grooves 23 and 24 out or radial alignment with the bead 25 of said tube section, a single elongated throat having a small cross-sectional area will be formed by the elongated groove 24 whereby the volume 22 in communication with said throat will attenuate a low range of frequencies. If the two adjacent Iinserts are maintained in this axial orientation, but are rotated with respect to each other to align the grooves 24 and 25, a single elongated Ythroat having a larger cross-sectional area will be formed whereby the volume in communication therewith will attenuate a higher range of frequencies. However, if the two adjacent inserts 'are forced together a distance'only sufficient to dispose the closed end of the groove 23 on one beyond the belled end of Vthe other, both kof the grooves 23 and 2A- will form throats so that the volume in communication therewith will attenuate an even Ihigher range of frequencies, :and by rotating the inserts with respect to throats may each yotherfto dispose one of the beads 23 or 24 in alignyrnent with the bead 25 while they are in thisaxial orientation a still higher rahge of frequencies will be attenuated.

Thus, the several resonatin-gV chamber volumes `and be individually tuned to not upon a widel range of frequencies, including the diicult to silence range of frequencies below 200 cycles per second. ln cer-tain instances, rfor example when .a series of the inserts ltare slidably joined together to provide the desired tuning eilect and thenfforced into theouter pipe lil, it may be desirable to weld or stake the inserts together to insure that the desired size and number of throats as 'well as 4the desired throat volume capacities are maintainedV when they areV fforced into position in the outer pipe.

As shown in FlG. 2, to support the neck end of the last insert in a series, a short insert is employed having only a bell 18 and a short tube section 16. In onder to permit a full range of tuning for the resonating chamber volume in operativey communication with this shortened terminal insert, it is7 of course, necessary that its tube section have a length at least equal to the neck Ztl of the insert over which it is press-lit and that it be provided with a `groove 25.

Although l have described the grooves 23v and 24 as being formed in the insert necks iand the grooves 25 in tube sections, it is, of course, possible to form the lgrooves 23 and 24 as .outwardly projecting grooves in the tube sections ld and the grooves 25 as inwardly projecting grooves in the necks. i It is also possible to employ .only single grooves in either the tube section-s or the necks, in which instance it will be possible to form only one throat at the junction Yofeach pair of inserts, the length oi? 'which can be adjusted to elect tuning.

A modified `form of my invention is illustrated in FIGS. 5-7 and comprises an outer pipe lil' .aud a plurality of interconnected inserts ld coaxially carried in said outer pipe and forming the main gas-flow pass-age. As shown, each of the inserts 14 is conveniently formed troni a length of metal-tubing and ycomprises an elongated tube :section 16 having an annular, outwardly projecting bell y18 at one of its ends. An elongated, open-ended, conM stricted neck Ztl' projects axially trom the opposite end of said tube section. The outer diameter of .the neck Ztl approximates the inner diameter of the tube section lr6 so that the neck 2:0 of one of said inserts may be pressrit into the tube section lr6 of the Vnext adjacent insert. In this manner, the interconnections between the adjacent inserts rare substantially gas-tight land the several inserts thus lform a continuous gas-how passage throughout Vtheir axial length in the outer pipe 10.

As shown in FIG. 5, the interconnected inserts 14' are maintained in a coaxial relationship within the outer pipe l0 by means of the bells 18', with each of said bells supporting the Yend of the insert upon which it is formed and the neck end of the next adjacent insert. As with the other modification oct any invention, each pair ott adjacent bells 18' denes the end walls of a resonatin-g chamber volume 22 having the conguration of ian extended annulus, the side walls of said volumes being f fornied by the outwardly presented walls of the inserts 14 :and the inwardly presented Wall of the pipe l0. `As shown in FIG. 5, the neck end of the last insert 14 in a series is supported vby a short insert having only a'lbell 18 and short tube section 16. Also shown in FIG. 5, the lirst insert 14 in a series will not have Ian insert received in its belled end, and its beads 26land 27 will not have an adjacent underlying surface with'which to torni a resonator throat; with the result that, unless la `sleeve having an aperture disposed in align-nient with said beads is inserted in the bellied end of the iirst insert, the resonator volume 22 lformed by said iirst insert merely serves as :different cross-sectional areas are formed on the tube 'section 16 adjacent the bell 18. Each of the beads 26 and 27 "extends around substantially the entire circumference of the tube section `16', but each has one of its ends closed as at 2.8 `and its opposite end open as at 30. An opening 32 having a width at least equal to the axial distance between the remote sides of the pair or beads is tormed in the neck 20 of each of the inserts in a position such that when a pair of the inserts 14 are disposed in interfitting engagement, the opening 32 on one ot said inserts will be disposed in alignment with either the bead 26, or 27, or both, on the other of said pair .of adjacent inserts. Thus, the beads 26 and 27 @form arcuate volume throats tor the resonating chamber volumes 22 :disposed within the axial extent of their respective tube sections, the openings Sli zand 32 constituting the terminal ends or" said throats.

To 4tune a pair of the inserts shown in FIGS. 5 and 7, the neck 20' of one of said inserts is slid into the belled end of the tube section 16 of the adjacent insert so that its opening 32 is disposed in the desired alignment with the beads 26 and 27 on said adjacent insert. It the ope-ning 32 is aligned with just one or said beads a single throat will be termed, and the two inserts may then be rotated -with respect to each other to adjust the arcuate spacing between the openings 32 and Sitil to thus provide the desired length for said throat for effecting the desired tuning. Of course, when a pair of inserts 'are rotated to dispose the opening 32 of one immediately adjacent the closed end 28 of one of thebeads'Z or 27 on the other, the longest possible single throat will be formed, and Vthe Volume 22' in communication therewith will attenuate extremely low bands of ltrequencies. By placing the opening 32 in alignment with both beads, a pair of throats are fonmed which may be tuned by rotating the inserts with respect -to each other to adjust the arcuate .spacing between the opening 32 and the open ends 30 0f the` two beads. As with the other modification of my invention, Where two throats are formed the volume 22' in communication therewith will attenuate a higher range ot frequencies than vvhere a single throat is employed. When the inserts are in the desired axial and rotational position Iwith respect to each other, they may be rigidly secured together as by welding and then placed in the outer pipe l0 to produce resonators attenuating at the desired range of frequencies.

Ot lcourse it is possible for either of the beads 2.6 or 27 to be open at both of its ends, that is at 28 and 30; in which instance that bead will -form |with the neck opening 32 a pair of throats acting in parallel. However, in such a situation the pair of throats act in combination with each other and the volume in communication therewith to produce, in effect, a single throat for said volume, said single throat having an effective length shorter than the actual length of either of the two .actual throats to thus cause the volume to attenuate a higher band of wave requencies than if the volume were in communication with only the shorter of the two throats.

It is of course possible Ito have an alternative construction of the insert 14 in which the beads 26 `and 27 project inwardly yfrom the neck 2d :and the opening 32 is formed in the tube section 16. And it is possible to step down the diameter of the belled end of the tube section i6 in which case the neck 2li will not have a restricted diameter, but due to the stepped down tube section diameter, the neck of one insert can still be press-lit into the tube section of an adjacent insert.

.As will be understood, when my invention is not used f as the sole means @for silencing the exhaust gases of an automobile engine, such as for example when it is used in combination with a conventional muiiler or as a component of such a muHer, lthe inserts are merely joined together to provide the desired tuning of the resonating chamber volumes and throats and are placed in a short length of lan outer pipe. These shorter outer pipes con- 6 taining the resonators may then be employed 'as sections of the exhaust pipes interconnecting the manifolds and muters, or used .as .components of conventional mulers, in Which case they are merely mounted within the outer muflier shells.

While my invention has been described for use in an exhaust system, it may, of course, be used on the intake side of an internal combustion engine for transporting and silencing the gaseous mixtures into the engine, or in any other 4applications involving the movement Iand silencing of gases.

I claim as my invention:

1. In a sound attenuating gas pipe ifor conveying and attenuating the noise level of a moving -gas stream, an outer pipe, a plurality of aligned inserts mounted within said outer pipe, each ofsaid inserts comprising a tube section having an axially projecting neck at one of its ends Iand an outwardly projecting bell at its opposite end, the neck on each of said inserts being inserted into the tube section of the next adjacent insert and supported against the inner |walls of said Itube section of said next adjacent insert to interconnect said inserts and form a main gas-flow passage, the bells on said inserts engaging the inner wall of the outer pipe to support the tube sections and necks of the inserts in spaced relation to the outer pipe .and define the end walls of a plurality ot resonator volumes interposed between the inserts and outer pipe, `and means on the interconnected ends of each pair or inserts forming at least one elongated open-ended throat joining Ione of said volumes to said main :gas-flow passage 4for attenua-ting the noise level of the `gas stream moving through said passage.

2. The invention as set 4forth in claim l in which the distance between the outer faces of the opposed walls of the necks approximates the distance between the inner taces of the opposed Walls of the tube :sections whereby said necks are press-lit into said tube sections to form `substantially Igastight joints between adjacent inserts.

3. The invention :as set forth in claim l in which said means are axially oriented on said inserts, and a plurality of said inserts are inserted different lengths into their next adjacent inserts to provide pluralities of volume-s ot different sizes and throats of dierent lengths.

4. The invention as set tooth in claim 1 in which said means are larcuately oriented on said inserts, and a plunality of said inserts are disposed in different angular orientations with respect to their next adjacent insents to provide a plurality of throats of different lengths.

5. The invention as set forth in claim 1 in which said means are axially and arcuately oriented on said inserts, and a plurality of said insents are inserted vdifferent lengths at dilerent angular orientations into their next adjacent inserts to provide pluralities of volumes of different sizes and throats of different lengths.

6. The invention as set forth in claim l in which said means on Athe interconnected ends of each pair of inserts 'comprises vat least one axially extending Igroove formed in the end of one of said pair of inserts `and the portion ot the side Wall of the other of said pair of inserts in alignment with said groove.

7. The invention las set forth in claim l in which said means on the interconnected ends of each pair of inserts comprises -a plurality of axially extending grooves of different axial lengths formed in the end -of one ot said pair of inserts and the portion ot the Iwalls of the other of said pair of inserts in alignment with said grooves, said pair of inserts being axially adjustable with respect to each other for adjusting the length .and number of said throats joining Asaid one volume to the main gas-ow passage.

8. The invention as set forth in :cl-aim l in which said means on the interconnected ends of each pair of inserts comprises at least one axially extending groove formed in the neck end of one of said pair of inserts and at least one axially extending groove formed in the belled end of 7 the `tube section ofthe Iother of said pair of inserts, said pair of inserts being axially `and rotatably :adjustable with respect to each other for adjusting the length and crossseotional area of the throat zformed by said grooves.

9. The rinvention as set forth in claim 1 in which said means Vonv thepi'nterconneoted ends of each pair of inserts comprises at least one arcuately extending bead formed on one of said pair of inserts adjacentan end thereof and the portion of the side Wall of the other of said pair of inserts in alignment with said bead, said bead having at least one opening disposed within the extent of one of said volumes and said side wall having an opening formed therein Within the extent of said bead.

and attenuating the noise level of a moving gas stream,

an outer pipe, a plurality of intertting, axially extending,

Vopen-ended inserts carried in the outer pipe and defining a main gas-flow passage, ,the axially extending walls of y said inserts being spaced from said outer pipe and acting k10.*The invention asset forth'in claim 9 in Which said bead extends substantially circumferentially ,around said one of said pair of inserts and has one of its ends closedY and its opposite end open.

11. The invention as setforth in claim 9 in which said pair of inserts are rotatably adjustable with respect to each other for adjusting the arcuate distance between said side wall and bead openings for adjusting the length of the throat formed by said pair of inserts.

'12. The invention as set forth in claim 9' in Which said side Iwall opening has a width at least as large as Y the width of the beaded area of said kone of said pair of inserts. Y y

13. Theinvention as set forth in Vclaim 1 in which said means comprises a plurality of outwardly projecting, arcuate beads formed on the tube section of one of said pair of inserts and the portion of the outer Wall of the neck of the other of said pair of inserts in alignment there-with, each` of said beads having an opening formed y f therein in communication with one of said volumes and said neck portion in alignment with the beads having an opening formed therein in communication with the main gas-flow passage.

14. The invention as set forth in claim 13 in which said plurality of beads are `axially spaced along said tube in combination with said outer pipe and means supporting said axially extending Walls in spaced relation to said outer pipe to form' a plurality of closed axially extending resonating chamber Volumes interposed between the main gas-110W passage and the outer pipe, and means on said inserts forming at the juncture of each pair of inserts at least one elongated'open-ended volume throat to dispose each of saidvolumes in operative communication with said main gaslow passage.

16. The invention as set forth in claim 12 in which said inserts are adjustably movable with respect to each other for adjusting the lengths of said throats.

References Cited in the ile of this patent UNITED STATES PATENTS Italy lune 19, 1957 

15. IN A SOUND ATTENUATING GAS PIPE FOR CONVEYING AND ATTENUATING THE NOISE LEVEL OF A MOVING GAS STREAM, AN OUTER PIPE, A PLUALITY OF INTERFITTING, AXIALLY EXTENDING, OPEN-ENDED INSERTS CARRIED IN THE OUTER PIPE AND DEFINING A MAIN GAS-FLOW PASSAGE, THE AXIALLY EXTENDING WALLS OF SAID INSERTS BEING SPACED FROM SAID OUTER PIPE AND ACTING IN COMBINATION WITH SAID OUTER PIPE AND MEANS SUPPORTING SAID AXIALLY EXTENDING WALLS IN SPACED RELATION TO SAID OUTER 